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Ultraviolet Light-Emitting Diodes: Challenges and Countermeasures
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Jun Hyuk Park, Jong Won Lee, Dong Yeong Kim, Jong Kyu Kim
Since LED is an optoelectronic device based on p–n junction, which converts electrical power to optical power, both electrical and optical properties are important factors determining the overall performance. Generally, highly doped n- and p-type semiconductor layers are required for desirable electrical and optical properties. N-type conductivity of AlGaN is achieved by incorporating Si atoms that substitute Al or Ga atoms in the lattice, providing loosely bound electrons. However, it is difficult to obtain high n-type conductivity in high-Al-content AlGaN due to large donor ionization energies and self-compensation effect. The ionization energy of the Si donors increases with increasing Al content, ranging from 15 meV for GaN to 62 meV for AlN, which is larger than the thermal energy at room temperature, leading to a highly resistive high-Al-content AlGaN (Neuschl et al. 2013; Park et al. 2016). Insufficient n-type doping in AlGaN exerts a harmful influence on LED performance including resistive ohmic contacts leading to a high operation voltage and poor EE. In addition, resistive n-type AlGaN layer intensifies the localization of the current path, so called “current crowding” effect. Current crowding induces local device heating and degrades the electrical and optical characteristics (Shatalov et al. 2002).
Basics of Semiconductor Detector Devices
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
This method is one of the most commonly used techniques to measure the quality of an ohmic contact, but does have a few potential problems. First, this method is based on the assumption that current flows uniformly from the contacts when, in reality, the current actually flows between the closest edges [Look 1989]. This non-uniform current is termed current crowding. To correct for current crowding, Look [1989] shows that the contact resistance is better described by Rc=RsρcWcoth(kL), where ρc is the specific contact resistivity under the metal-semiconductor interface, Rs is the sheet resistance under the contact, L is the contact length, and k2 = Rs/ρc. If kL≳2, then ρc is well approximated by ρc≃W2Rc2Rs.
Automotive Power Semiconductor Devices
Published in Ali Emadi, Handbook of Automotive Power Electronics and Motor Drives, 2017
Note that this energy is completely dissipated in the avalanched MOSFET, resulting in an increase in its junction temperature. The avalanche energy rating EAS of the MOSFET is the amount of energy allowed to increase the device junction temperature to the maximum junction temperature rating TJMAX, which is 175°C for this device. Repetitively exceeding TJMAX may cause concerns on the long-term reliability of the semiconductor device, but not necessarily instantaneous device failures. This is why the tested value of single pulse avalanche energy rating EAS(tested) is much higher than the thermally limited EAS. However, once the junction temperature of the MOSFET increases to a range of 330 to 380°C, several internal device failure mechanisms may be triggered to cause the collapse of the device breakdown voltage and eventually the catastrophic failure of the device. One of the failure mechanisms is the activation of a parasitic BJT as an integral part of the MOSFET structure, as shown in Figure 6.9. The NPN parasitic bipolar transistor is formed among the N+ source (“emitter”), the P-body (“base”), and the N-type drain (“collector”). During normal operation of the MOSFET, this BJT is inactive since its base and emitter are shorted by the source metal of the MOSFET. However, when the body diode between the drain and P-body of the MOSFET is in avalanche mode, a large avalanche current will flow through the P-body and induce a voltage drop across the P-body resistance (“base resistance”). If this voltage drop exceeds 0.7 V, the emitter-base PN junction will be forward biased at certain locations and initiate the BJT activation process. Once activated, the BJT will demonstrate a snapback negative resistance characteristic, resulting in the collapse of the MOSFET breakdown voltage. It may subsequently lead to current crowding in localized areas and molten silicon or metal interconnects in these “hot spots.”
Improved transmission line model for high-frequency modelling of through silicon vias
Published in International Journal of Electronics, 2019
Vasileios Gerakis, Alkis Hatzopoulos
To visualize the proximity effect, two parallel TSVs of 2.5 um radius, 50 um height and at a 15 um pitch, were simulated in ANSYS HFSS for frequencies up to 50 GHz. The TSV on which the ports were placed is considered as the Signal-TSV (STSV) and the neighbouring is considered as the Ground-TSV (GTSV). The current flows from the GTSV to the STSV through a planar metal path (see Figure 1) covering a 15 um pitch. The current density pictured in Figure 2 indicates that the proximity effect leads to current crowding between the two TSVs. It also shows that as the frequency increases, the STSV current concentrates at the side that faces the GTSV (front) leaving the other side with lower current density (back). In the case of the 50 GHz, there is a red area (high current density) at the front side, while it is a green one at the back. So, the proximity effect is not only apparent but depends also on frequency, so a model should include the frequency as an independent variable.